Water flow rate (or pressure) drop question

  • #1
Hi, I'm not sure if I'm posting in the right spot but I'm going to guess this is an easy question for you all. I'm going to give as much detail as I can, maybe too much..

My 2 family house condo has a single 2" or 3" water supply from the street. It is split to supply the first floor and second floor. Until recently, the split to each floor stepped down to a 1/2" copper pipe, a section of the upstairs neighbors pipe cracked, it was replaced with 3/4" flexible pipe. On the first floor, I noticed an drop in water flow (or pressure, not sure but, the water comes out of the shower slower so I think flow).

There are water meters for each floor, after the split but before the step to 1/2" and 3/4 pipe.

A few question please, If the pipe size is different for each floor, is the flow/pressure affected?

If there is no demand on the second floor(3/4 pipe) will the flow/pressure increase on the first flow? (I assume no because of the meters, they wouldn't allow water to flow back and worth,- this may also lead to the answer to the first question, yes, the larger pipe will "steal" flow rate or pressure?)

I really hope my questions are clear. Ill provide any more information if needed.

Thanks In advance, SinTax

Answers and Replies

  • #2
A change in pressure will change the flow and vice versa. Since the main supply is so large relative to the branches it is more likely something changed other than branch pipe size. You might look at the valves near and at the meters to assure one was not left partially closed. Even though your half was not repaired, valves may have been closed and not fully reopened. Also debris/rust may have been disloged and clogged the screen in your shower head.

Good luck!
  • #3
The pipe to the second flow will steal flow/pressure from the first floor only if water is flowing to the 2nd floor. The pipe to the first floor will steal flow/pressure form the second floor only if water is flowing to the 1st floor.

  • #4
Montoyas and Chet, thanks for replying. I'm going to check everything you've suggested.
  • #5
I looked at the meters (Badger RTR model 25), if I'm reading the dial correctly, the second floor reads, .95 cubic meters the first floor reads .77 cubic meters

Does this mean anything to you guys? I don't have the readings prior to the work being done. I am hoping these numbers can show a higher flow or pressure to the 2nd floor. I'm not sure if that would cause the first floor to drop in pressure.
  • #6
Ok sorry, it's cubic feet and the needle indicates %of ten gallons. Not flow or pressure.
  • #7
All else being equal, if they didn't change your pipe size, or the connecting pipe between the main and your piping, you should not see a difference in pressure than previously. Similar to Chestermiller's point, the only difference you might see would be if both yourself and your neighbor were running water at the same time. It is possible that the larger pipe in their walls result in a lower back-pressure than your system which would result in them taking a larger share of the water than previously while both systems are running. However given that they are above you, and that I can't imagine they replaced all of their piping, I find it unlikely that it would be noticeable.

More likely your showerhead has scaling/buildup or there are additional blockages/leaks in the existing piping.

Meters are don't regulate flow, they measure it.
  • #8
I was thinking the meter would show flow rate or pressure. What I am seeing happened right after the work was done. This is why I think it's related to the pipe diameter change caused it. But the replies to my post make sense. I'll check for debris since that's l I can really do.

No work was done to pipes in the walls. were able to see all the new pipe.

Thanks again for responding. I'll post anything I find. If you have any other thoughts or questions that may help determin an answer, please let me know.
  • #9
The larger pipe to their side could result in additional flow due to reduced friction. This increased flow rate would be balanced by slightly higher losses in the main pipe, which could potentially drop the pressure going to your floor.

But realistically, a small section of 3/4" pipe vs 1/2" is not going to make a noticeable difference...

Nope, those meters basically just read the total flow that has gone through them so that utility companies can manage water usage (and billing!)

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